The invention is in the field of multiple photoflash lamp arrays and last-flash indicators for indicating when the last lamp has been flashed.
An example of a commercially available mutliple flash lamp array, known as FlipFlash, is described in U.S. Pat. No. 3,935,442 to James M. Hanson, and comprises an upper group of lamps connected electrically to a connector plug at the bottom of the array adapted to plug into a camera socket for providing flash-firing pulses to the array. Circuitry in the array includes switches respectively actuated by lamps when flashed so as to cause sequential flashing of the lamps, one at a time, in response to the firing pulses. A lower group of flash lamps in the array is connected electrically to a connector plug at the top of the array, so that when the lamps of the upper group have been flashed, the array is turned over and the "lower" group of lamps becomes the upper group which then are flashed. By flashing only an upper group of lamps, in each of the flash array's two positions on the camera, the array reduces the undesirable red-eye effect in which a person's pupils tend to appear red or pink if the flashing lamp is too close to the camera lens. The above-referenced patent also discloses flash indicators at the back of the array which change color as the lamps are flashed, thus indicating how many lamps have been flashed and how many have not been flashed.
It would be convenient to have a last-flash indicator visible in the camera viewfinder to indicate when the last lamp of the array has been flashed, and in the case of a FlipFlash type of array to indicate when the last lamp of each half (or group) of the array has been flashed so that the user will be informed that the array should be turned over or a new array should be plugged into the camera.
Several ways have been proposed for providing a last-flash indicator in a camera viewfinder for various types of multiflash units. U.S. Pat. No. 3,380,357 to Donald M. Harvey discloses an arrangement of four indicator lights for indicating how many flash lamps have been flashed in a flashcube using filament-type lamps. Also, U.S. Pat. No. 3,583,841 to Donald M. Harvey discloses an arrangement of indicator lights for indicating how many flash lamps have been flashed in a flashcube using percussively fired lamps. U.S. Pat. No. 3,707,903 to Kurt H. Weber and U.S. Pat. Nos. 3,668,421 and 3,714,407 to Harry J. Bowers, Jr., disclose arrangements of flashcubes and flash arrays having last-flash actuating rods for actuating a movable last-flash indicator visible in a camera viewfinder.
The above-referenced patent application discloses a multiple flash array of the FlipFlash type having sequencing circuitry for causing the lamps to flash one at a time in response to firing pulses applied to a pair of input terminals of the array. A normally open or high resistance switch means is connected electrically across the pair of input terminals and electrically closes or becomes a relatively low resistance in response to flashing at the last-to-flash lamp, so as to electrically actuate a last-flash indicator in the camera, via the input terminals of the array.